The industrial production of vitamin B.sub.12 by chemical synthetic methods is difficult because of its complex structure. Fermentation processes using microorganisms have been used for its production.
It is reported that vitamin B.sub.12 is produced by microorganisms belonging to the genera Streptomyces, Norcardia, Micromonospora, Aerobacter, Agrobacterium, Alcaligenes, Azotobacter, Bacillus, Clostridium, Corynebacterium, Escherichia, Flavobacterium, Mycobacterium, Pseudomonas, Propionibacterium, Proteus, Serratia, Streptococcus, Xanthomonas, Protaminobacter, Methanobacillus (E. J. Vandamme, Biotechnology of Vitamins, Pigments and Growth Factors, Elsevier Science Publisher LTD, 1989, 261-263), Arthrobacter (JP-A 52-94498), Klebsiella (JP-A 50-132186), Rhodopseudomonus (JP-A 60-16597), Butyribacterium (JP-A 62-44197), Pseudonocardia (JP-A 55-96091), Methanosarcina (JP-A 1-257490), Eubacterium (JP-A 62-44172), Acetobacterium (JP-A 62-122593), etc. Further, it is reported that vitamin B.sub.12 is accumulated by microorganisms belonging to the genera Rhizobium meliloti, Rhizobium phaseoli, Rhizobium japonicum, Rhizobium trifolli and Rhizobium leguminosarum (Plant Physiology, 38, 99-104 (1963)).
Of the above microorganisms belonging to the genus Rhizobium, Rhizobium phaseoli and Rhizobium trifolli have been renamed Rhizobium leguminosarum (see Institute for Fermentation, Osaka, Japan, List of Cultures 1992 Microorganisms, 9th edition, p. 169). A part of Rhizobium japonicum has been renamed Rhizobium leguminosarum and the rest has been re-classified into Bradyrhizobium japonicum (see Institute for Fermentation, Osaka, Japan, List of Cultures 1992 Microorganisms, 9th edition, p. 169).
However, in general, microbial processes produce vitamin B.sub.12 in very low yield. Further, some microorganisms can utilize limited carbon sources (methanol assimilating bacteria, etc.), need special cultivation conditions such as anaerobic conditions (propionibacteria, microorganisms belonging to the genus Acetobacterium, methane producing bacteria, etc.), need long cultivation because of their low growth rates (methane producing bacteria, propionibacteria, etc.), and therefore can be used for industrial production only under limited conditions. Thus, improved industrial methods of producing vitamin B.sub.12 are desired.